W10 - Emotion Flashcards
What is emotion?
- Emotional expression
– Animal and human studies - Emotional experience
– Human studies - Affective Neuroscience
– neural basis of emotion and mood
– (mood as an emotion extended in time)
How can you test for anxiety in rats?
Increase of anxiety-like behaviour following long-
term opioid abstinence
You can put a rat on an elevated cross like apparatus with one covered and protected segment and the other an open segment. Let the rat explore for a few mins and observe where it is most likely to explore in that time frame. Spends about 30% of the time in open arms.
If injected with a benziodiazepine drug, which is an anxiolitic drug, it would spend a lot more time in the open arms in comparison.
How do you test for depression in animal models?
Increase in depressive-like behaviour following
long-term opioid abstinence.
Forced swim test:
Take a 5L beaker and fill it with water.
Put the mouse in there and let it swim for 7-10 mins in the water.
At first, it would swim happily in the beaker. Then, after a while, it would get fed up and try to get out of the beaker. Once it realises it can’t, it will resort to a freezing behaviour, where it would only have just enough movement in the hind legs to keep the head afloat.
All antidepressant are tested using this forced swim test. These drugs should decrease the immobilised state of a mouse.
How do you measure expressions of emotions through sociability behaviour in mice?
Long-tem morphine abstinence abolishes social
preference.
This experiment needs a 3-chambered box with a connected door.
In two of the chambers, there needs to be cages.
In one of these cages, there needs to be another mouse, while the other one is empty.
You put the test mouse in the box and measure the time it spends socialising vs the time it spends alone.
They spend a lot more time in the social chamber because they are social animals.
In morphine absent mice, indifference was shown, where they spend an equal amount of time in both chambers, suggesting it was not interested in socialising.
What are the brain mechanisms of emotion?
- Emotions:
– Love, hate, disgust, joy, shame, envy, guilt, fear, anxiety, etc. - What defines emotions?
- Theories of emotion:
– James- Lange - We experience emotions in response to physiological changes in our body. Eg. when we cry, we get sad. Lots of holes in this theory.
– Cannon-Bard - We can experience emotions independently of emotional expression (dissociations)
– Emotions are produced when signals reach the thalamus either directly from sensory receptors or by descending cortical input
What are the James-Lange vs. Cannon- Bard theories?
- The James–Lange theory: emotion experienced in response to physiological changes in body
- The Cannon–Bard theory: emotions occur independent of emotional expression—no correlation with physiological state
Is there a brain system responsible for Emotions?
- Broca’s Limbic lobe
– Limbus (latin) means border
– primitive cortical gyri that form a ring around
the brain stem - Broca’s limbic lobe includes
– the parahippocampal gyrus
– the cingulate gyrus
– the subcallosal gyrus
What is the limbic system?
- Broca’s limbic lobe
– Areas of brain forming a ring around corpus
callosum: cingulate gyrus, medial surface
temporal lobe, hippocampus
Later discovered, all these areas are involved in emotional processing.
What are the limbic structures associated to the Papez circuit?
- Limbic structures, including cortex, involved in emotion
- Emotional system on the medial wall of the brain linking cortex with hypothalamus
When we respond to stimuli, the emotional colouring takes place in the Neocortex.
This is in connection to the Cingulate cortex - where emotional experience takes place.
This stimulus is propagated to the hippocampus.
This is connected to the Hypothalamus via a number of neurones called the fornix. Hypothalamus then expresses emotion.
The neurones then signal to the anterior nuclei of thalamus, which then circles back to the Cingulate cortex.
This means emotional experience triggers expression vise versa.
What is The Papez Circuit
- Cortex critical for emotional experience
- Hippocampus governs behavioural expression of emotion
– Rabies infection implicates hippocampus in emotion -> hyperemotional responses - Anterior thalamus
– Lesions lead to spontaneous laughing or crying. - Paul MacLean popularised the term limbic system.
– Evolution of limbic system allows animals to experience and express emotions beyond stereotyped brain stem behaviours.
What is the Limbic system as we define it?
- Cingulate gyrus
- Parahippocampal structures
- Septal nuclei
- Amygdala
- Enthorinal cortex
- Hippocampal complex
– dentate gyrus
– CA1-CA4 subfields
– subiculum
What is the function of the limbic system?
- Anatomically the limbic system appears to
have a role in attaching a behavioral
significance and response to a stimulus,
especially with respect to its emotional
content - Damage to the limbic system leads to
profound effects on the emotional
responsiveness of the animal - Cingulate gyrus
– role in complex motor control
– pain perception
– social interactions-mood - Hippocampus proper and
parahippocampal areas
– primary function in memory (critical role in
connecting certain sensations and emotions
to these memories) - Amygdala
– involved in learning and storage of emotional
aspects of experience
What is the limbic system by definition?
- Difficulties with the single emotion system
concept
– Diversity of emotions and brain activity
– Many structures involved in emotion - No one-to-one relationship between structure and function
– Limbic system: use of single, discrete emotion
system questionable
What are the Emotion Theories and Neural
Representations?
- Early theories of emotion and limbic system
built on introspection and inference from
brain injury and disease. - Studies of disease and consequences of
lesions not ideal for revealing normal
function. - More recent theories of emotion
– Basic emotion theories
– Dimension emotion theories
How do we measure neurological activity in our brain now?
We have scanners now where we can measure people’s brain activities while they feel a certain emotion.
In fMRI scanners, they found emotions are associated with distinct patterns of brain activity - signatures.
Eg. Sadness was more associated with activities of the prefrontal cortex.
Eg. Fear = More association with amygdala.
What is the amygdala?
- Greek word for almond - it is an almond like structure.
- Critical structure for emotion in particular
– fear and aggression, anxiety
What tests were done to explore the link between the amygdala and emotion?
Healthy human volunteers were taken in and placed in fMRI scanners and exposed them to different images of facial expressions.
Neutral expression = normal amygdala activity
Fearful expression = amygdala really lights up
What are the structures and connection of the amygdala?
- Receives input from neocortex (Where colouring of emotions take place)
– All lobes, including hippocampal, and cingulate gyri (where emotions are experienced) - Basolateral nuclei
– Receives information from all sensory systems - Corticomedial nuclei
- Central nuclei
- Output to hypothalamus (region involved in expression of emotion)
– Stria terminalis
– Ventral amygdalofugal pathway
What is the fear of amygdala?
- The Kluver-Bucy syndrome (rhesus
monkeys) - Temporal lobe removal of those monkeys (temporal cortex, amygdala, hippocampus) and they observed their behaviour.
– Good visual perception but poor visual
recognition
– psychic blindness
– oral tendencies - started putting objects in mouth.
– emotional changes (reduced fear) - eg. let humans stroke them or didn’t mind snakes.
– altered sexual behaviour - hypersexual
How is fear induced?
- Amygdalectomy (humans)
– Reduce fear
– Reduce Aggression
– Hypersexuality
– Oral tendencies
– Reduce ability to recognize a fearful expression (can recognise happiness)
– Flattened emotions - Electrical stimulation
– Increased vigilance
– Anxiety
– Fear
– Aggression
What is learned fear?
- Amygdala involved in forming memories of
emotional and painful events - Confirmed by fMRI images and PET imaging
Rabbits were conditioned with electric shocks. Whenever they heard a specific tone, they get an electric shock. After a while, they would get scared of the sound without the shocks.
The somatosensory and auditory cortex gets stimulated by the sound and shocks. This sends signals to the basolateral amygdala. This activates the central nucleus of the amygdala. This induces neural plasticity. This leads to the projection of the signals to the:
- Hypothalamus = autonomic response
- Periaqueductal gray matter in brain stem = behavioural reaction
- Central cortex = Emotional experience
How is past experience integrated?
Amygdala and the integration of current stimuli
and past experience
(A neural circuit for learned fear)
* Amygdala involvement in giving emotional content to memories (fear conditioning)
* Involved in PTSD
What is aggression?
- Multi facetted behaviour (kill for freedom, murderer, power, dominance)
- Endocrine mechanisms (testosterone, castration)
- Brain mechanisms
– Predatory aggression - Attacks made against a member of a different
species, to obtain food - No sympathetic activity
– Affective aggression - For show, threatening posture
- Social hierarchy
- High levels of sympathetic activity
– Amygdala important role in aggression related to social hierarchy
How is the amygdala associated with aggression?
- Surgery to reduce human aggression
– Amygdalectomy
– Psychosurgery—now treatment of last resort - Results
– Reduced aggressive behavior
– Relief from anxiety
– Profound, unpleasant side effects - Karl Pribram (rheusus monkeys, humans)
- Amygdala removal
– Transformation from dominant to subordinate
(social hierarchy, reduced agression)
What is the neural component of anger and
Aggression Beyond the Amygdala?
Experiment on cats.
- The hypothalamus and aggression
– Removal of cerebral hemispheres (cats) but not hypothalamus -> sham rage, extremely angry and violent.
– Remove both cerebral hemispheres + anterior
hypothalamus -> sham rage - Also remove posterior hypothalamus -> No sham rage
- Electrical stimulation of hypothalamus leads to affective and predatory aggression
How is the hypothalamus associated with aggression?
- Flynn’s research of cats
– Elicited affective aggression by stimulating medial hypothalamus.
The cat started hissing, arching back etc in response to the mouse, but did not kill it.
– Predatory aggression elicited by stimulating
lateral hypothalamus
No more vocalisation of hissing - silently went to bite the mouse.
What is the Neural Circuit for Anger and Aggression?
- Two hypothalamic pathways to brain stem involving autonomic function
– Medial forebrain bundle -> connection between hypothalamus and ventral tegmental area; predatory aggression
– Dorsal longitudinal fasciculus -> connection between hypothalamus and periaqueductal gray matter; affective aggression
What is a strongly associated neurotransmitter with aggression in primates? How does it work?
- Serotonin deficiency hypothesis
– Aggression is inversely related to serotonergic activity. - 5HT antagonist increase aggression
- Agonists of 5HT1A or 5HT1B decrease anxiety
and aggressiveness - In humans also, reports of negative correlation
between serotonin activity and aggression
